An optical member in an Organic Light-Emitting Diode (OLED) display device includes a linear polarization plate, and a λ/4 phase-difference plate, both of which primarily function as anti-reflection in the OLED display. For example, when natural light passes the linear polarization plate, the natural light parallel to an absorption axis of the linear polarization plate passes the linear polarization plate through a linear sheet, and the natural light perpendicular to the absorption axis of the linear polarization plate is shielded by the linear polarization plate; and after the natural light passing the linear polarization plate passes the λ/4 phase-difference plate, the natural light passing the λ/4 phase-difference plate will be turned into elliptically polarized light and circularly polarized light due to the π/2 phase delay between the azimuth of a fast axis and the azimuth of a slow axis of the λ/4 phase-difference plate; and if there is a 45° angle between the absorption axis of the linear polarization plate and the slow axis of the λ/4 phase-difference plate, as illustrated in FIG. 1, then after the natural light passes the linear polarization plate and the λ/4 phase-difference plate, the natural light will be turned into right-rotated circularly polarized light, and the right-rotated circularly polarized light will be turned into left-rotated circularly polarized light after being reflected on a metal electrode; and after the left-rotated circularly polarized light passes the λ/4 phase-difference plate, the left-rotated circularly polarized light will be turned into linearly polarized light which is perpendicular to the absorption axis of the linear polarization plate, and then the linearly polarized light cannot pass the linear polarization plate.
However, there are the following characteristics of the polarization sheet and the phase-difference plate in the OLED display in the related art:
The inverse wavelength diffusion characteristic of the single layer phase-difference plate tends to fail to agree with the ideal characteristic, as illustrated by the conventional QWF in FIG. 2, due to different phase compensations by the phase-difference plate for light in different wavelength bands, as denoted in Equation (1):Rte=nyd=(θ/2π)λ  (1)
where Rte represents a phase compensated in the direction of the slow axis; θ represents a compensation phase angle; and ny represents an in-plane refractive index in the direction of the slow axis.
It can be determined in Equation (1) that, if incident light is in a short wavelength band, then there will be a large phase compensation; and if the incident light is in a long wavelength band, then there will be a small phase compensation, as illustrated by the conventional QWF curve in FIG. 2. For the ideal value in FIG. 2, Rte is in direct proportion to λ, and it can be apparent from Equation (1) that the compensation phase angle is same for different wavelength bands, so that light in all the wavelength bands will be completely absorbed by the optical member.
Both the linear polarization plate and the λ/4 phase-difference plate in the optical member are prepared for light at the 550 nm wavelength, that is, incident blue light at 550 nm can be completely absorbed by the optical member, but light in the other wavelength bands will be partially reflected, so that reflection cannot be completely cancelled. Reflectivities of predominant products in the market at present range between 2% and 6%.
The organic layer in the OLED device emits light with various phases, e.g., linearly polarized light, elliptically polarized light and circularly polarized light. If the absorption axis of the linear polarization plate in the optical member in the OLED display is parallel to the slow axis of the λ/4 phase-difference plate, and there is a 45° angle between the absorption axis of the linear polarization plate and an optical axis of the linear polarization plate, as illustrated in FIG. 3, then when the organic layer of the OLED device emits linearly polarized light, i.e., a light ray as illustrated in FIG. 3, the linearly polarized light is turned into right-rotated circularly polarized light after passing the λ/4 phase-difference plate for the first time, and when the right-rotated circularly polarized light passes the linear polarization plate, only a component P light parallel to the absorption axis of the linear polarization plate can pass and a component S perpendicular to the absorption axis of the linear polarization plate can not pass the linear polarization plate; here the P light refers to light perpendicular to the λ/4 phase-difference plate, and S light refers to the light parallel to the λ/4 phase-difference plate, and natural light can be regarded as the combination of these two components of light. When the organic layer of the OLED display emits circularly polarized light, i.e., b light ray as illustrated in FIG. 3, the circularly polarized light is turned into linearly polarized light after passing the λ/4 phase-difference plate for the first time, here the linearly polarized light is distributed in respective vibration directions, so only a part of the linearly polarized light can pass the linear polarization plate; and when the organic layer of the OLED display emits elliptically polarized light, i.e., c light ray as illustrated in FIG. 3, the elliptically polarized light is turned into linearly polarized light after passing the λ/4 phase-difference plate for the first time, here the linearly polarized light is distributed in respective vibration directions, so only a part of the linearly polarized light can pass the linear polarization plate. It can be determined from the analysis above, the light with the respective phases emitted from the organic layer in the OLED display will be at least attenuated to half in brightness after passing the optical member in the OLED display.
In summary, the optical member in the existing OLED display may suffer the problem of loss in transmitting light, hence it is difficult to improve the transmittivity of the light therein.